1. Field of the Invention The present invention relates to an image signal processing apparatus, and more particularly to an image signal processing apparatus which produces an image signal suitable for image reproduction.
2. Description of the Prior Art
In an output device such as a printer or a display which receives a digital or analog image signal, particularly in an output device which displays an image by a combination of output dots of several gray levels by using a dither method, a strong beat is generated when a frequency of the input signal has a specific relation with a frequency of the output dot pattern due to a fold-over error in sampling by an input device, as to well as a periodicity in the output dot pattern. Such a beat appears as a hinders clear perception of the image and substantially deteriorates image quality. This is known as a Moire phenomenon. Attempts have been made to reduce harmful frequency components by optical or electrical techniques eliminate the Moire pattern.
In this method, however, since not only the harmful frequency components but also high frequency components are reduced, the output image is not sharp.